Under the proposed effort, the feasibility of an implantable telemetry device for the chronic monitoring of blood volume flow in conscious, unrestrained animals will be studied. The main focus of this effort will be the evaluation of several well-established approaches to monitoring blood flow and their potential for incorporation in an implantable device with small size and low power consumption. As a minimum design goal, the device should be capable of reliably measuring relative flow with 10% accuracy at one site in dogs and non-human primates for a period of at least 350 hours. Adaptation of this device for application in rodents is a secondary goal. During the project alternate designs will be investigated, first conceptually and then via breadboard models. In vitro tests will be used to initially evaluate flow measurement accuracy of alternate designs. The preferred design will then be assessed in vivo to verify flow measurements on different vessels sizes and flow rates. A requirements analysis will also be conducted for an integrated implantable transmitter capable of measuring blood flow, pressure, heart rate and ECG. Although no such equipment is commercially available at present, recent developments in both integrated circuit and battery technology may now make a cost-effective device feasible.